In power systems, a lightning impulse is a sudden surge of electricity due to lightning event. It can disrupt the normal flow of electricity in power lines, potentially damaging critical equipment like power/distribution transformers. This will lead to power outage causing inconvenience to the end user. Breakdown of the dielectric media which is oil in case of wet type transformers is complex phenomena as compared to dry type where the dielectric media is air. Breakdown mechanisms in air such as streamer inception propagation and leader propagation have been extensively investigated by researchers in the past. Whereas breakdown in bulk oil is not heavily worked upon. Hence, transformer designers have very few tools at their disposal, one of them being FEA simulation. The lightning impulse is a transient phenomenon which is difficult to simulate in 3D FEA domain. A novel approach is being proposed which combines 2D/3D electrostatic simulation and industry defined design curves to assess the robustness of transformer design. This research paper talks about two approaches. In first approach, a simplified 2D approach is followed to understand the electric field along the shortest creepage path between HV and LV windings. This electric field stress is then compared with an impulse design curve derived from Weidman design curves with an appropriate impulse factor. Secondly, a detailed 3D simulation is performed using Ansys Maxwell to check the critical locations where maximum field stresses are going beyond breakdown strength of oil. In the current work, simulation was performed on oil type high voltage kV class distribution transformer and results show that the transformer design is passing lightning impulse test. This is corroborated with the actual lightning impulse with the same transformer. This simulation approach will help transformer designer to design a dielectrically robust transformer.